Add the following lines to the top of your Matlab script (not Slurm script); e.g. the xyz.m file

% create a local cluster object
cluster = parcluster('local')

% start matlabpool with max workers set in the slurm file
parpool(cluster, str2num(getenv('SLURM_CPUS_ON_NODE')))

A sample Matlab submission file can be found on the FIU HPC at this location